This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Iron-sulfur clusters are ubiquitous in nature and participate in many biochemical processes. Incorrect cluster configurations result in disease, hence it is imperative that we understand how they are synthesized. Almost all organisms have evolved a specialized, multi-component protein system to ensure correct FeS cluster assembly. In Eschericia coli this system consists of the proteins IscU, IscA, IscS, HscA and HscB. Available experimental evidence strongly suggests that IscU acts as a scaffold for the assembly of FeS clusters while the molecular chaperones HscA and HscB assist in the transfer of this cluster to target apo-proteins. We are using NMR spectroscopy to create structural models of the HscB:IscU and the HscA(SBD):IscU complexes in order to gain new insight into how this transfer process occurs.